The present invention relates generally to integrated circuits, and more particularly to power-on reset circuits.
In many typical electronic applications, it is desirable to reduce power, for example, to manage thermal or battery powered operating budgets. Reducing power may involve minimizing the amount of current drawn by elements of the circuit. One way of lowering an average operating current of a circuit is to provide power down modes, which deactivate portions of the circuit while not in use. When these circuits power back up, however, they may need to power-up in a known state.
Powering up circuits in a known state may be accomplished by using a power-on reset (“POR”) circuit to provide a reset signal to the circuit. For example, when a portion of the circuit is in power-down mode, the operating voltage may drop, causing the reset signal to be provided in a low state. When the portion of the circuit powers back up, the operating voltage rises, ultimately crossing some threshold level (e.g., a minimum voltage level at which memory portions of the circuit can operate normally), causing the reset signal to switch to a high state. Implementing this POR circuit functionality may involve contending with at least three concerns: shrinking operating voltages, CMOS process compatibility, and temperature sensitivity.
As critical dimensions for integrated circuits continue to shrink, the maximum operating voltage of the circuits also may decrease. Lower operating voltages may tend to prevent large electric fields from damaging the circuit structures such as gate oxide, diffusion depletion regions, and various insulating layers. Therefore, it is often desirable to manufacture integrated circuits in advanced semiconductor technologies to be capable of operating at low voltages, thereby providing compatibility with the maximum operating voltages of particular semiconductor technologies.
At these shrinking operating voltages, the voltage margin available to the POR circuit to make the ‘above’ or ‘below’ decision may be reduced, increasing the importance of making more accurate voltage level detection. As such, achieving accurate voltage level detection may become increasingly difficult as the operating voltage decreases. Also, because a POR circuit continually monitors the supply voltage, it is active during power-down modes. Thus, it may be desirable for the POR circuit to draw extremely small amounts of current, for example, to extend battery life.
Thus, it may be desirable to provide a POR circuit that is relatively accurate even in low voltage environments, while also consuming relatively small amounts of power.